Various analytical instruments have been developed for making optics-based measurements (e.g., fluorescence, luminescence, and absorbance) on samples (e.g., chemical compounds, biological material, etc.) as part of assays useful in the life science industry. Many analytical instruments are designed to carry out only one or a few dedicated types of measurements. On the other hand, multimode analytical instruments, also referred to as multimode readers, are designed to perform multiple analytical assays in a single instrument. Multimode analytical instruments may be designed to be re-configurable to enable a user to select different types of measurements to be performed. Some multimode analytical instruments utilize application-specific cartridges to enable re-configuration.
Some types of measurements, such as fluorescence and absorbance measurements, require that the sample be irradiated with a beam of light, referred to herein as “excitation” light. In the case of fluorescence measurements, the excitation light is needed to induce fluorescence in the sample. In a typical example, the sample is irradiated with excitation light of a relatively short wavelength, and in response emits fluorescent light of a relatively longer wavelength. This “emission” light is measured by a suitable light detector, which often is a photomultiplier tube (PMT) in the case of fluorescence measurements. In the case of absorbance measurements, the excitation light is needed when the absorbance measurement is based on comparing the amount of the excitation light transmitted through the sample versus the amount of the excitation light incident on the sample. Measurements requiring excitation light may further require that the excitation light utilized to irradiate the sample be limited to a specific wavelength or very narrow band of wavelengths. In the case of fluorescence measurements, the fluorescent response may require a specific excitation wavelength. In the case of absorbance measurements, the light detector utilized (often a photodiode in the case of absorbance measurements) may have an optimum sensitivity at a certain wavelength or very narrow band of wavelengths.
Thus, wavelength-selection devices have been utilized in the excitation light path (as well as the emission light path) of optical-based analytical instruments. Wavelength-selection devices include monochromators and optical filters, the design and operation of which are familiar to persons skilled in the art. It is also known that advantages and disadvantages are associated with both monochromators and optical filters. Depending on the type of measurement to be performed, the type of sample under analysis, and other factors, one type of wavelength-selection device may be preferred over others. In some situations, it would be useful to employ two different types of wavelength-selection devices (e.g., a monochromator and an optical filter) in tandem, while in other situations it would be useful to employ one type of wavelength-selection device while bypassing the other type of wavelength-selection device.